2.1. ACQUIRED IMMUNE DEFICIENCY SYNDROME
Acquired immune deficiency syndrome (AIDS) has in recent years become a major focus of health related research in the United States, and similar attention is beginning to be devoted in other countries as well. The disease, which is caused by a retrovirus known as human immunodeficiency virus (HIV-1), has reached near-epidemic proportions in the U.S., and at the present time there is no known cure. AIDS in its most advanced stages is characterized generally by a suite of ailments which have typically been associated with individuals whose immune system has been compromised or actively suppressed by drug administration. Among these diseases which are infrequently observed in immunologically normal individuals is Kaposi's sarcoma, a rare form of skin cancer, and numerous opportunistic infections such as Pneumocystis carinii pneumonia, toxoplasmosis, histoplasmosis, cryptococcosis, and cytomegalovirus. Occasionally, infection may be associated with a debilitating condition referred to as AIDS-related complex (ARC) which is characterized by unexplained fevers, night sweats, chronic diarrhea, and wasting. Although the present understanding of the mode of action and ultimate effects of the virus are in no way complete, it is generally understood that the virus preferentially infects and destroys helper/inducer T lymphocytes, specifically those known as OKT4.sup.+ or T4 cells. These T4 cells are involved in orchestrating cell mediated immunity by influencing the activity of cytotoxic cells such as T8 lymphocytes and natural killer cells. T4 cells also influence the activity of monocytes and macrophages which engulf infected cells and foreign particles, and also produce cytokines. The decline in T4 cell populations can be observed relatively early in the progress of an HIV infection. The loss of these helper T cells severely impairs the body's ability to mount an immune response against the intracellular pathogens which ultimately give rise to the opportunistic infections which characterize this disease; however, deficiencies in nearly all aspects of the host defense system have been observed in patients with AIDS.